CORS Checker tests whether a cross-origin request from your site would be allowed by the target server. Runs the preflight (OPTIONS) and actual request, reports an ALLOWED/BLOCKED verdict, and breaks down Access-Control-Allow-Origin, Methods, Headers, and Credentials so you can pinpoint exactly why a request is failing.
"Blocked by CORS" is one of the most confusing errors in browser development — the browser silently prevents the request without returning useful information to your code, and reading raw CORS headers is tedious. CORS Checker makes the whole picture clear. Enter the target URL, HTTP method, and the origin you want to test as (defaults to your current page). Optionally list any custom request headers you plan to send (content-type, authorization, etc.). The tool then runs the preflight OPTIONS request (automatically added when the request isn't "simple") followed by the actual request, and parses every relevant CORS response header. It then renders a pass/fail breakdown: is Allow-Origin set correctly, does Allow-Methods include your method, are your custom headers in Allow-Headers, does Allow-Credentials match your credentials flag? The final verdict is unambiguous — ALLOWED or BLOCKED — and the per-check list tells you exactly what to fix on the backend.
Detects when a preflight OPTIONS request would run (non-simple methods or custom headers) and fires it automatically with the correct Access-Control-Request-* headers.
Each CORS rule is evaluated individually: origin match, allowed methods, allowed headers, credentials. You see exactly which check fails.
Big green ALLOWED or red BLOCKED banner at the top — no reading headers to figure out the answer.
Shows every response header from both preflight and actual requests, with CORS-specific headers highlighted.
Pretend to be any origin, not just the current page — useful for testing how third-party integrations would be handled.
The probe runs from the extension background so cross-origin fetches are not blocked by the host page's own CORS policy.
When your frontend shows a CORS error in the console, use the tool to see exactly which header the backend is missing — much faster than reading spec sections.
Before shipping a new public API, test it from the tool to confirm every expected origin, method, and header combination works.
When integrating with a third-party API, test from your origin with your planned headers to confirm the request will go through.
Check the Access-Control-Max-Age value to see how long the browser will cache preflight results — useful when testing after header changes.
Run the same CORS test against dev, staging, and prod URLs to catch environment-specific misconfigurations before users do.
Click the CORS icon in the DevSuite Pro dock. A panel opens with URL, method, origin, and headers inputs.
Paste the API endpoint you want to test and pick the HTTP method (GET, POST, PUT, DELETE, etc.).
Origin defaults to the current page. Change it if testing a different origin. List any custom request headers comma-separated.
The tool runs the preflight (if needed) and the actual request, then renders the verdict and checks.
If BLOCKED, the per-check list tells you what's missing from the server's response. Fix the backend header and re-test.
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